Rotor warp: Solid vs. fluted?

Status
Not open for further replies.
Joined
Apr 10, 2016
Messages
1,255
Location
Campbellsville, KY
Noting the other day, while having the front wheels off my '82 Mercedes for the first time, that it has solid rotors all the way around rather than the more common type with cooling fins between the two friction surfaces - will a solid rotor withstand more heat than a hollow one before becoming unusable? Now, you may say, the solid one won't cool as well so it'll get hotter in the first place; this may be true. But what of the initial question?
 
I had factory Mercedes rotors on my 83 240D.....never had a warp problem.....but I used factory rotors. Things are tanks.
 
Vented. I'm surprised to see solid rotors on an MB, the last other vehicle I saw with solid rotors anywhere was a 79 Mazda. Vented rotors dissipate heat WAY faster (even faster than drilled/slotted solid rotors), and are actually more rigid because the internal vanes lock two external disks together, making a sort of trusswork that is extremely rigid.

FWIW, rotors don't warp, at least not unless you get them INSANELY hot. Like NASCAR at Bristol rotors-glowing-orange-in-the-corners hot.

Most "warped" rotors are perfectly flat, but have unevenly accumulated deposits from the pads outgassing- it usually starts with someone making an aggressive stop and then sitting at a light for a minute or two with the hot pads clamped hard against the hot rotors.

I've had cars that you'd swear the rotors looked like Ruffles potato chips the way the wheel shook when you touched the brakes. One scotch-brite wheel on a die grinder lightly applied to both sides of the rotor while turning the rotor by hand, and then rinsing with Brakeleen... cured. Years ago, I couldn't believe it when I first read that this was the usual cause of "warped" rotors, but after trying simple cleaning and de-glazing a dozen times over the years, I'm 100% convinced. Now, every time I change pads, I de-glaze and rinse the rotors and I've never had the problem since. I'm also a fan of EBC brake pads which come with an abrasive break-in coating that keeps the rotors from glazing as the new pads bed. And they'd probably break the glaze on old rotors without any manual labor, but I always do my manual de-glazing instead.
 
I will have to try deglazing my rotors next time.

I've had serious vibration in the STI while braking. Replacing the rotors completely stopped any vibration.

I have done it twice now. Currently I have slotted and drilled rotors, so maybe there will be less build up on those.

Previously the OEM Subaru ones were smooth, and I replaced them with a set of smooth aftermarket ones.
 
Originally Posted By: 440Magnum


FWIW, rotors don't warp, at least not unless you get them INSANELY hot. Like NASCAR at Bristol rotors-glowing-orange-in-the-corners hot.

Most "warped" rotors are perfectly flat

Around 95% of the cars and trucks that come into the shop I work at, when they have a pulsating brake pedal, at least one of the rotors are in fact warped. I can't even begin to count how many times I have placed a suspect rotor on a flat metal surface, and was able to rock it back and forth. I live in northern New York State, and it seems like in the winter the salt used on the roads, plus the extreme difference in temperature the brakes see really tears them up.
 
Last edited:
Every small/compact car I had (with small diameter and width wheels) have seen some warped rotor at some point in life. On the other side, the wide wheels car I had, or the wife’s SUV, haven’t seen any warped rotors yet. Maybe something to do with discs diameter (dissipation area) or the protection from eater splashes?
 
I even had warped rotors on motorcycles. Sometimes heat/cooling factor, sometimes forgot to remove antitheft disc lock device
crazy.gif


Then comes overtorquing wheel nuts... seen it on bitog
 
Originally Posted By: wheelman1991
Originally Posted By: 440Magnum


FWIW, rotors don't warp, at least not unless you get them INSANELY hot. Like NASCAR at Bristol rotors-glowing-orange-in-the-corners hot.

Most "warped" rotors are perfectly flat

Around 95% of the cars and trucks that come into the shop I work at, when they have a pulsating brake pedal, at least one of the rotors are in fact warped. I can't even begin to count how many times I have placed a suspect rotor on a flat metal surface, and was able to rock it back and forth. I live in northern New York State, and it seems like in the winter the salt used on the roads, plus the extreme difference in temperature the brakes see really tears them up.


I currently have this going on in the Journey. This will be it's 3rd winter and while the pads still have 40% life left the rotors pulsate like crazy when braking moderately. I'm just putting up with it until the pads are done and then I will replace it all and most definitely after the winter.
 
Originally Posted By: StevieC
Originally Posted By: wheelman1991
Originally Posted By: 440Magnum


FWIW, rotors don't warp, at least not unless you get them INSANELY hot. Like NASCAR at Bristol rotors-glowing-orange-in-the-corners hot.

Most "warped" rotors are perfectly flat

Around 95% of the cars and trucks that come into the shop I work at, when they have a pulsating brake pedal, at least one of the rotors are in fact warped. I can't even begin to count how many times I have placed a suspect rotor on a flat metal surface, and was able to rock it back and forth. I live in northern New York State, and it seems like in the winter the salt used on the roads, plus the extreme difference in temperature the brakes see really tears them up.


I currently have this going on in the Journey. This will be it's 3rd winter and while the pads still have 40% life left the rotors pulsate like crazy when braking moderately. I'm just putting up with it until the pads are done and then I will replace it all and most definitely after the winter.


I'm telling you, just try de-glazing. You will be astounded. The whole crux of the matter is that a little warpage WON'T make the pedal pulse or the wheel wobble unless a caliper is also seized. Deposit buildup will. The calipers float with a small amount of warpage. Uniform thickness is mandatory, but rotors don't have to be (and won't stay) absolutely perfectly flat.
 
I can't be bothered taking them a part to do this, I will ride them like this and then just replace them. If it happened with almost new pads then I would for sure but these are almost used up anyway.
 
My observations lead me to believe both are possile. Warpage with consistent thickness shouldn't cause pulsing because the caliper can float. But, if heat is so rarely what kills a rotor, why does turning a shaky rotor (removing those deposits of foreign material) so seldom produce a lasting fix?
 
Last edited:
Unless you take before and after runout readings, you'll never really know if your rotors warped, or went on crooked in the first place.

EVERY SINGLE TIME I ask "what was your runout when installed" of someone who claims "warped rotors" I get NO ANSWER.

“Without data, you're just another person with an opinion.” -W. Edwards Deming

No, you won't know at first, until the friction material embeds sufficiently on the high spots to give you that wuba-wuba feeling when you hit the brakes.

Every single modern factory service manual I've seen has instructions for measuring on-vehicle runout as part of a brake job. The number of times it has been performed by dealers or mechanics for me? Zero. But ALL of them are happy to tell you "your rotors warped" (that is, YOUR FAULT) when you come back in.

I've had ZERO problems with "warped rotors" since I started measuring runout on each and every brake job. I have returned a few rotors, though.
 
Originally Posted By: Alex_V
My observations lead me to believe both are possile. Warpage with consistent thickness shouldn't cause pulsing because the caliper can float. But, if heat is so rarely what kills a rotor, why does turning a shaky rotor (removing those deposits of foreign material) so seldom produce a lasting fix?
Pad transfer again. Turning just removed the old stuff. You haven't done anything to prevent the real problem.
 
Originally Posted By: Alex_V
But, if heat is so rarely what kills a rotor, why does turning a shaky rotor (removing those deposits of foreign material) so seldom produce a lasting fix?

Several reasons.
1. Turned rotors are installed without checking on-vehicle runout. That is, a perfectly flat, true rotor can be mounted crooked. I see it, well, every single brake job I do. I have to index the rotor, clean the hub, in one case I had to remove a feature (broken off Honda machine screw nub) to get the rotor to near zero runout.

2. Parallelism is not checked on the turned rotor. So it may be near-perfectly flat on each side, but not those two sides may no longer be in parallel.

Either issue will cause a return of pad buildup. (That, or poor break-in).

My personal experience is that:
a. The vast majority of rotors pass off-vehicle runout and parallelism specs when new;
b. Not so many pass after being turned;
c. Every brake job I do requires some kind of corrective action to bring on-vehicle runout within factory spec.

It has also been my observation that most every brake job in this country is done without the parallelism and on-vehicle runout checks being done. You can easily see this when I ask for as-built runout mesaurements in forums and get zero answers (well I did get one or two recently).
 
Originally Posted By: 440Magnum
Originally Posted By: StevieC
Originally Posted By: wheelman1991
Originally Posted By: 440Magnum


FWIW, rotors don't warp, at least not unless you get them INSANELY hot. Like NASCAR at Bristol rotors-glowing-orange-in-the-corners hot.

Most "warped" rotors are perfectly flat

Around 95% of the cars and trucks that come into the shop I work at, when they have a pulsating brake pedal, at least one of the rotors are in fact warped. I can't even begin to count how many times I have placed a suspect rotor on a flat metal surface, and was able to rock it back and forth. I live in northern New York State, and it seems like in the winter the salt used on the roads, plus the extreme difference in temperature the brakes see really tears them up.


I currently have this going on in the Journey. This will be it's 3rd winter and while the pads still have 40% life left the rotors pulsate like crazy when braking moderately. I'm just putting up with it until the pads are done and then I will replace it all and most definitely after the winter.


I'm telling you, just try de-glazing. You will be astounded. The whole crux of the matter is that a little warpage WON'T make the pedal pulse or the wheel wobble unless a caliper is also seized. Deposit buildup will. The calipers float with a small amount of warpage. Uniform thickness is mandatory, but rotors don't have to be (and won't stay) absolutely perfectly flat.


Agree, I've never had a warped rotor. Always glaze spots from slamming the brakes.. on the highway.. on a hot summer day.

Or.. cheap rotors that get hot and fry pads (turning removes heat dissipating metal, making glazing more likely).

Or.. The space between hub and rotor had some buildup. So the rotor does dot sit evenly on hub. I complained to Raybestos about a warped rotor, they sent me this device complimentary. OMG that worked!!!
 
Status
Not open for further replies.
Back
Top